This invention relates to a novel method for the preservation, packaging and shipping whole fruits, fresh-cut salads and fresh-cut flowers. More particularly, this invention pertains to novel methods to prolong shelf life of packing whole fruits, fresh-cut salads and fresh-cut flowers in modified atmospheres packaging with the addition of nitric oxide (NO). The nitric oxide is added to the modified atmosphere at the time the package is sealed.
The quality attributes of freshly harvested fruits, vegetables (called xe2x80x9cproducexe2x80x9d) and cut flowers need to be maintained after harvest to ensure produce reached the consumer in an acceptable condition. Quality deterioration of harvested horticultural produce is caused by a range of natural reactions such as respiration, ripening and senescence, through microbial growth and by evaporation of water. Methods of inhibiting the rate of deterioration from all causes include reduction of the produce temperature, and creation of a low O2/high CO2 modified atmosphere (MA) around the produce
Modified atmosphere packaging (MAP) of fruits, vegetables and horticultural products involves packing produce in a sealed but gas-permeable package system and generating the MA by introducing a gas comprising a predetermined ratio of CO2 and O2 into the headspace of the package or allowing the natural respiration of the produce to develop desired levels of CO2 and O2 in the headspace of the package. During storage, the wall permeability of the MAP system regulates the influx of O2 relative to the efflux of CO2 from the package headspace to achieve and/or maintain a suitable MA equilibrium in the headspace around the stored produce. This establishes an optimum environment for retention of the quality attributes of the fresh produce and reduces detrimental microbial growth in the produce.
There are, however, many problems in maintaining the optimum levels of CO2 and O2 inside a package that maximize the retardation of deterioration, and hence maximize the postharvest life of the produce. One problem can be due to difficulty in maintaining the desired temperature throughout the marketing and transport chain of the MAP package. A common scenario is for the temperature to be considerably higher than the optimum. A higher temperature radically changes the modified atmosphere inside the MAP with the CO2 rising and the O2 decreasing in concentration. This increases respiration of the produce at the higher temperature and accelerates deterioration. Such changes in atmosphere can be outside the safe CO2 and O2 levels and result in the development of off-flavors, undesirable browning of tissues and a general reduction in postharvest life of the produce. Where temperature variations are likely to occur in the marketing of produce, a prudent MAP operator will opt to have a lower level of CO2 and higher level of O2 than the optimum in the MAP to provide a safety margin for changes in atmosphere due to changes in temperature during marketing. The end result is that the extension time in postharvest life achieved by the MAP is less than would be achieved if the optimal modified atmosphere is used.
A second problem arises from difficulty in achieving an identical modified atmosphere in all boxes of produce in a batch of seemingly uniform produce. Variation will occur due to differences in maturity and hence respiration or degree of ripeness within a batch of produce, differing degrees of microbial contamination, variability in the permeability of the package film and outer container, as well as different degrees of sealing a package. The overall effect is that a range of atmospheres will be generated in any batch of MAP. In order to ensure that an unsafe extreme atmosphere is not developed, the best MAP will have the optimum atmosphere to retard deterioration but all others will have a suboptimal modified atmosphere to varying degrees with associated shortened postharvest life.
Thus, while properly controlled low O2 levels and elevated CO2 levels in the MAP headspace around a fresh fruit, vegetable or cut flower reduce the respiration and ripening rate of the fresh produce, and the growth of spoilage organisms, and leads to a slower the rate of deterioration of produce, the effect is still only a slowing of metabolism. Some loss of quality is still occurring, albeit, at a much reduced rate. When the use of sub-optimal atmospheres occurs, either by design or accident, the reduction in the rate of deterioration is even less pronounced.
These variability factors therefore create the potential for the use of additional treatments that can, independently of the modified atmosphere, exert a beneficial effect in retarding loss of quality in harvested horticultural produce.
Ethylene generation is an important factor in the deterioration of fresh fruit, vegetables and cut flowers. Ethylene is well known to accelerate deterioration in horticultural produce. These effects are seen by initiation of premature ripening, acceleration of loss of colour and texture, induction of microbial growth, induction of physiological disorders and other browning symptoms.
Ethylene is generated by all horticultural produce. When produce is held in ambient air, the ethylene concentration is relatively low due to dilution in the atmosphere. However, in the confined space of postharvest containers, such as in a MAP, ethylene can accumulate to relatively high concentrations. Traditionally, a threshold concentration of 0.1 xcexcL/L ethylene is considered a safe limit of ethylene exposure. However, recent studies in Australia on a wide range of horticultural produce has shown there is no safe level of ethylene exposure and that concentrations of ethylene greater than 0.005 xcexcL/L generate a deleterious response. Across the whole range of concentrations, it has been found that the rate of deterioration of horticultural produce increases with increase in ethylene concentration.
The level of ethylene that accumulates in a MAP can be quite high with concentrations in the range 1-10 xcexcL/L commonly encountered in commercial practice. While a modified atmosphere does give some inhibition of the deleterious effects of ethylene, it has been found that an ethylene concentration of 1 xcexcL/L around cut lettuce held in a MAP reduces the effective postharvest life of the lettuce by 50%. Thus, the use of a technology that inhibits the action of ethylene on produce held in a MAP would provide an additional extension to the useful postharvest life of fresh fruit, vegetables and cut flowers independently of the modified atmosphere.
Australian. Patent No. PCT/AU98/00799 discloses an invention to extend the postharvest life of perishable horticultural produce stored in ambient air through the short term fumigation with low concentrations of nitric oxide gas prior to storage. A typical effective treatment is cited as placing produce in a fumigation chamber for 2-6 hours in an atmosphere containing 5 xcexcL/L nitric oxide and a very low concentration of oxygen. After the treatment, the produce is stored in a ambient air conditions containing ethylene at concentrations found in normal horticultural marketing situations. The postharvest life of produce fumigated with nitric oxide is purportedly extended by 20-200% over untreated produce and the rate of water loss is purportedly reduced by 15-30%. The benefit of the treatment is attributed to inhibiting the action of ethylene on the horticultural produce.
The invention is directed to a method of prolonging the postharvest life of a perishable horticultural produce after harvest which comprises placing the produce in a package with a modified atmosphere and adding nitric oxide to the modified atmosphere.
The nitric oxide can be injected into the modified atmosphere of the package after the package is sealed. The nitric oxide can be added to the package in an amount which provides a concentration of nitric oxide in the modified atmosphere of the package of between 1.0 and 200 xcexcL/L. The nitric oxide can be permitted to remain in the package until the package is opened for marketing. The horticultural produce can be fruit, vegetables or cut flowers.
The invention is also directed to a modified atmosphere package containing a perishable horticultural produce, and a postharvest produce life prolonging modified atmosphere containing oxygen, carbon dioxide and nitric oxide. The modified atmosphere can contain a below ambient atmosphere level of oxygen and an above ambient atmosphere level of carbon dioxide. The concentration of nitric oxide can be between 1.0 and 200 xcexcL/L.